Ring opening of cyclohexane over ZSM-zeolites followed by reversed-flow gas chromatography

Summary Kinetic parameters for the ring opening of cyclohexane over modified ZSM-5 zeolites can be measured simultaneously under non-steady state conditions using reversed-flow gas chromatography. At relatively low temperatures, the main product detected and measured was propene.The mathematical relations used for the calculation of adsorption-desorption rate constants, surface reaction rate constants and adsorption equilibrium constants for the reactant cyclohexane are different from previously studied catalytic reactions, owing to the different experimental arrangement for feeding the catalytic bed. The diffusion bands obtained experimentally for reactant or product are described by the sum of two or three exponential functions of time, respectively. From the exponential coefficients of time and the pre-exponential factors, all determined by simple PC programs, the above kinetic parameters are calculated.     

Ring opening of cyclohexane over ZSM-zeolites followed by reversed-flow gas chromatography

Summary Kinetic parameters for the ring opening of cyclohexane over modified ZSM-5 zeolites can be measured simultaneously under non-steady state conditions using reversed-flow gas chromatography. At relatively low temperatures, the main product detected and measured was propene. The mathematical relations used for the calculation of adsorption-desorption rate constants, surface reaction rate constants and adsorption equilibrium constants for the reactant cyclohexane are different from previously studied catalytic reactions, owing to the different experimental arrangement for feeding the catalytic bed. The diffusion bands obtained experimentally for reactant or product are described by the sum of two or three exponential functions of time, respectively. From the exponential coefficients of time and the pre-exponential factors, all determined by simple PC programs, the above kinetic parameters are calculated.     

A differential method for the analysis of chemical kinetics results based on reversed-flow gas chromatography

Summary The reversed-flow gas chromatographic technique has been applied to the determination of the apparent rate constant and the reaction order of a reaction between two gases or vapors. For seven hydrocarbons (ethane, ethene, ethyne, propene, butene, benzene and toluene) reacting with nitrogen dioxide, the above mentioned kinetic parameters have been determined. For these determinations, the necessary mathematical formulation of the problem has been written and solved, leading to simple expressions which describe the height of the chromatographic sample peaks as a function of time.     

Physicochemical quantities in catalytic reactions measured simultaneously by gas chromatography

Summary A small volume of reactant, 1-butene, is injected onto a catalytic bed and is allowed to diffuse away from it together with the product butane, along a narrow empty chromatographic tube; the latter is connected perpendicularly to the middle point of another similar tube through which hydrogen flows as reactant and carrier gas, transferring both 1-butene and butane to the detector through an analytical column. By using the reversed-flow GC technique, extra peaks are obtained in the chromatographic trace, sampling the concentration of both the readtant and product at the junction of the two tubes as a function of time. These concentrations are the result of the diffusion of the substances along the narrow empty tube, modified by the adsorption-desorption rates and the rate of the catalytic reaction. From the extra peaks of the reactant and product, a number of physicochemical quantities pertaining to the catalytic reaction can be calculated simultaneously, using appropriate mathematical analysis. These include adsorption rate constants, reaction rate constants, desorption rate constants, partition coefficients, and the overall mass transfer coefficients of the reactant across the gas-solid boundary of the catalytic bed. Presented at the 17th International Symposium on Chromatography, September 25–30, 1988, Vienna, Austria.     

Kinetic study of the drying step of supported catalysts by reversed-flow gas chromatography

Summary Application of reversed-flow gas chromatography to study the drying step in the preparation of supported catalysts is proposed. It is demonstrated that this technique can be applied to investigate the kinetic law followed, as well as to obtain kinetic parameters of drying (rate constants, activation energies and frequency factors). Amaterial illustrating this application is -Al₂O₃ impregnated with usual organic solvents (n-C₅H₁₂,n-C₆H₁₄,n-C₇H₁₆, CH₃COCH₃ and CH₃CH₂OH). It was found that in all cases above a simple first-order law based onone kind of active site is followed. Moreover, it was observed that the activation energyE _a of the drying process increases almost linearly with the relative molecular mass of the solvent, whereas for the same solventE _a increases with the amount used. The operation of a kinetic compensation effect suggests similar activated complexes of the various solvents used.     

Estimation of solubility and interaction parameters in binary liquid mixtures by reversed-flow gas chroamtography

Summary A new method, called reversed-flow gas chromatography, is presented for the measurement of the gaseous equilibrium concentrations of all the components under study, both in the pure state and in binary liquid mixtures. From the equilibrium concentrations, activities, activity coefficients and volume fraction activity coefficients were determined. Using various empirical equations relating activity with the molecular interactions between the components of a binary liquid mixture, the solubility parameters of ethanol, 1-propanol, acetone and methylethylketone in water were calculated. The total interaction parameters and the partial contributions of the dispersion, orientation and residue forces on the van der Waals attraction between the organic compounds and water were also computed. The variation of the interaction parameters with the composition of organic component in the binary mixture was investigated. The successful application of reversed-flow gas chromatography to the estimation of polymer solubility parameters is also reported. Finally, the solubility parameters found by the present method are compared with those determined by other techniques or calculated theoretically.     

Measurement of diffusion coefficients in multicomponent gas mixtures by the reversed-flow technique

Summary The reversed-flow method for measurement of gas diffusion coefficients in binary mixtures is now extended to simultaneous determination of effective diffusion coefficients for each substance in a multicomponent gas mixture. The method is applied to six ternary mixtures, each consisting of two gaseous hydrocarbons and H₂, He or N₂. The results are in agreement with a limiting case of the Stefan-Maxwell equations.     

Solvent retention in thin polymer films studied by gas chromatography

Thin polystyrene films were produced by spin coating from solutions in toluene. The amount of solvent retained in the films after drying for different times was measured using gas chromatography. Whereas for thicker films (thickness > 200 nm), the relative amount of solvent in the films is less than a few percent, the proportion of toluene increases significantly in thinner films. The thickness dependence of the mass of retained solvent shows that the solvent is mainly retained at the polymer–substrate interface. The solvent desorption rate exhibits no variation on the film thickness.     

Chromatographic determination of the rate and extent of absorption of air pollutants by sea water

Summary A simple chromatographic method is developed to determine the rate constant for expulsion of an air pollutant from water or its diffusion parameter in the liquid, the rate constant for chemical reaction of the pollutant with water, its mass transfer coefficient in the liquid, and the partition coefficient between liquid water and air. From these physicochemical parameters, the absorption rate by sea water and, therefore, the depletion rate of a polluting substance from the air can be calculated, together with the equilibrium state of this absorption. The method has been applied to nitrogen dioxide being absorbed by triple-distilled water and by sea water, at various temperatures. From the temperature variation of the reaction rate constant and of the partition coefficient, the activation energy for the reaction and the differential heat of solution were determined.     

Flux of gases across the air-water interface studied by reversed-flow gas chromatography.

In the present work the reversed-flow gas chromatographic technique was applied for the study of flux of gases across the air-water interface. The model system was vinyl chloride-water, which is of great significance in food and environmental chemistry. Using suitable mathematical analysis, equations were derived by means of which the following physicochemical quantities were calculated: diffusion coefficient of vinyl chloride (VC) into water, partition coefficient of VC between the water (at the interface and the bulk) and the carrier gas nitrogen, overall mass transfer coefficients of VC in the gas (nitrogen) and the liquid (water), gas and liquid film transfer coefficients of VC, gas and liquid phase resistances for the transfer of VC into the water, and finally the thickness of the stagnant film in the liquid phase, according to the two-film theory of Whitman. From the variation of the above parameters with temperature, as well as the volume and the free surface area of the water, useful conclusions concerning the mechanism for the transfer of VC into water were extracted. These are discussed in comparison with the same parameters calculated from empirical equations or determined experimentally by other techniques.     

Measurement of activity coefficients in polymer solutions by the reversedflow technique

Summary The reversed-flow, gas-chromatographic method for measuring activities and activity coefficients in binary liquid mixtures is now extended to the determination of activity coefficients of the solvent in polymer-solvent systems over the whole range of polymer concentration, as well as for the calculation of Flory-Huggins interaction parameters. The parameters found by the present method are compared with those determined by other techniques or calculated theoretically.     

邻氨基苯腈气相色谱分析法的研究

采用邻苯二甲酸二壬酯为固定液,Chromsorb W/AW为载体的色谱柱和热导检测器,用苯乙腈为内标物,对邻氨基苯腈试样进行了分析,其中邻氨基苯腈的回收率为100.5%,试样浓度小于1%时测定的相对标准偏差小于8.6%。     

国内气相色谱近年的进展

本文对近三年国内学者在气相色谱方面的研究和应用作了综述 ,国内学者的研究基本和国际上气相色谱方面的研究类似 ,在全二维气相色谱、快速气相色谱 ,微型气相色谱仪、新型气相色谱固定相和色谱柱的溶胶 凝胶涂渍技术领域的研究方面作出了贡献。有关气相色谱的应用研究中 ,介绍了大量在药物分析、食品分析、环境分析、石油和石化分析和化工产品及高聚物分析等领域中应用的题目和摘要     

Direct injection on capillary columns for gas chromatography

Discrimination may occur when injecting samples onto gas chromatography capillary columns, whereby peak areas for higher boiling point compounds are smaller than they should be compared to lower boiling compounds. This problem is most important in quantitative work on solutes having a wide range of volatility. An all-glass inlet system was used. Injections were made with a 10-μl syringe onto a column without and injection point heater and with the column oven about 20°C below the boiling point of the solvent used for the solutes. Discrimination did not occur in a range of C₁₂ to C₃₆ n-alkanes.     

Gas chromatographic determination of rate constants in bimolecular gaseous reactions

Summary Rate constants for bimolecular reactions in the gas phase, under diffusion controlled conditions, can easily be determined by the reversed-flow gas chromatography (RF-GC) technique. The analysis of the diffusion band by means of a simple PC programme gives directly an apparent, second-order rate constant for gaseous reactions. By varying the amounts of the reactants, one can calculate the true order of the reaction and the true non-first-order rate constant of gaseous reactions. The calibration problem of the analytical techniques in non-first-order reaction kinetics is absent as are other disadvantages connected with carrier gas flow, peak shape and their instrumental spreading. The method can be used for atmospheric reactions and was applied in the gaseous reaction systems: SO₂+NO₂, SO₂+Br₂, C₆H₆+NO₂, C₆H₅CH₃+NO₂ and C₃H₆+NO₂ with various concentrations of reactants in nitrogen. The effect of the NO₂ concentration on the apparent second-order rate constant of C₂H₄+NO₂ at 333.2 K was also studied. Finally, the effect of sun light pre-irradiation of C₂H₂+NO₂ in nitrogen was investigated.     

Fast analysis by gas chromatography

Summary The efficiency of fast GC columns depends largely on the quality of the chromatograph. A theoretical and experimental study shows the relative importance of the various phenomena involved and permits the optimization of a GC System. Extremely good performances, exceeding 2,500 plates per second have been routinely obtained.Ezzel a tanulmánnyal Halász István Professzor Urat köszöntjük 60. születésnapja alkalmából.